Due to the action of tectonics,a rock slope often loses stability under the joint action of several weak structural planes.Its failure form is quite different from that of a single weak structural plane.Especially under the reciprocating action of earthquakes,its stability analysis is very complex, and it needs appropriate criteria to judge its stability state. In view of the strong objectivity of plastic strain energy,which can truly reflect the stability of rock and soil mass,this paper analyzes the stability of slope under earthquake action by establishing the relation curve between plastic strain energy and reduction coefficient of rock slope with structural plane of composite weak structural plane in a practical hydraulic project after the earthquake, taking the sudden change of plastic strain energy after the earthquake as the criterion of instability. Then we compare the calculation results with the results of the displacement mutation and the plastic zone penetration criteria. The results show that the sudden change criterion of plastic strain energy is close to the results obtained by the sudden change criterion of displacement of characteristic points and the breakthrough criterion of plastic zone.The accuracy is guaranteed,which is not affected by subjective factors such as the selection of observation points. The results obtained are unique,providing a better choice for the analysis of dynamic stability of rock slopes with combined weak structural planes.